1. Field of the Invention
The present invention relates to semiconductor devices, and more particularly, to a method for forming a metal line of a semiconductor device having a favorable orientation, namely, a <111> orientation.
2. Discussion of the Related Art
Metallization is a process for connecting respective components of a semiconductor device with a low resistance by forming contact portions on the semiconductor device to connect inner circuits of chip and package. The metallization metal should exhibit excellent adhesion to a thin layer, such as a silicon (Si) or silicon oxide (SiO2) layer, and exhibit a high conductivity when reacted with silicon. The metallization metal should also resist heat and mechanical stresses. The metal should also have low resistance for ohmic contacts and should exhibit good ohmic contact properties with respect to inner circuits.
When such a metal is used in a metallization for forming a metal line on the semiconductor device, the metal line must have a strong resistance to corrosion and oxidation. The metal line must also resist the problems of electron migration and stress migration. Aluminum, rather than other noble metals, is the most widely used material, since aluminum exhibits excellent adhesion to silicon or silicon oxide, can realize a good ohmic contact with heavily doped n+ or p+-silicon, has a low specific resistance of about 2.7 μΩcm, and is inexpensive.
Due to high integration of commercial semiconductor devices including DRAM, metal lines are reduced in width and suffer from easy cut-off of the metal wire. The cut-off of the metal wire is due to collision between electrons and aluminum ions upon migration of the electrons through the aluminum line.
In general, when an aluminum layer is deposited by sputtering, it has defects such as hillocks or dislocations, which deteriorate electrical properties when electrons migrate through the aluminum layer.
In addition, annealing is generally performed at a temperature of approximately 400 to 450° C. after deposition of an aluminum alloy. During this process, silicon is non-uniformly diffused from a bonding interface between the aluminum layer and a silicon substrate to the aluminum layer.
As a result, silicon is gradually consumed to cause a reduction in the bonding area, and the aluminum layer infiltrates into the silicon layer in order to fill a vacancy caused by the non-uniform diffusion of silicon. A spike-shaped portion is thereby formed. When a high electric field is applied to the spike portion, the bonding between the aluminum layer and the silicon substrate is broken, causing an increase in current leakage and thus deteriorating the properties of the semiconductor device.
FIGS. 1A and 1B are cross-sectional views of an aluminum line of a semiconductor device fabricated according to a related art method.
As shown in FIG. 1A, an insulating layer 12, a lower reflection preventing layer 13 of titanium/titanium nitride (Ti/TiN), and an aluminum layer 14 are sequentially deposited on a silicon wafer 11. An upper reflection preventing layer 15 of titanium/titanium nitride is formed on the aluminum layer 14.
As shown in FIG. 1B, the upper reflection preventing layer 15, the aluminum layer 14, and the lower reflection preventing layer 13 are selectively removed by photoresist and etching processes to form an aluminum line 20 having a desired width.
An interlayer insulating layer (not shown) is then formed over the entire surface of the semiconductor substrate 11 as well as the aluminum line 20 and is selectively removed to form a contact hole (not shown). Thereafter, another aluminum line (not shown) is formed to electrically connect to the aluminum line 20 through the contact hole.
The related art aluminum line has been developed as a semiconductor line irrespective of a copper line. In particular, the aluminum used is under a 0.13 μm design-rule in order to maintain reliability. As the width of the aluminum line is narrowed, however, a gap-filling problem occurs in subsequent inter-metal dielectrics. The gap-filling problem generally necessitates a thinning of the aluminum line. The reduction in width of the aluminum line also increases its resistance so that sufficient current cannot be supplied. Furthermore, as an operating voltage is reduced due to miniaturization of transistors, a specific resistance of the aluminum line becomes a serious issue.